Vehicles may be configured with defrosting systems to clear condensation and/or thaw frost from the windshield, back window, and/or side windows of the vehicle. Defrosting systems may include components, such as blowers and fans that are shared with a vehicle heating ventilation and air conditioning (HVAC) system and an engine cooling circuit. For primary defrosting, heat is provided by the vehicle's engine coolant via the heater core. Specifically, fresh air is blown through the heater core and then ducted to and distributed over the interior surface of the windshield by a blower. In addition to fans and blowers of the HVAC system, an air conditioner may also be operated during defrosting to dehumidify the air blown by the fans and blowers. The dehumidification makes the defrosting more effective and faster since dried air has a greater capacity to absorb water from the glass at which it is directed. Secondary defrosting, often used on the back and/or side mirrors, typically consists of multiple resistive conductors embedded in or on the glass. When power is applied, these conductors heat up, thawing ice and evaporating condensation from the glass.
The inventors herein have recognized potential opportunities with the defrosting mode. As an example, the engagement of the air conditioner to dehumidify the cabin air results in condenser heat being rejected to the atmosphere during cold ambient conditions. This heat is lost to the environment without being used. The inventors have recognized that this heat can be harnessed instead of being lost to the environment. Cold ambient conditions can also overcool the refrigerant (or coolant) in the cooling circuit and create freezing concerns. Since the defrosting mode requires hot air that has been heated via the engine cooling circuit, efficient defrosting may be delayed until the engine has sufficiently warmed. Ironically, since engine heat is sent to the cabin to heat the cool air, engine warm-up during defrosting may be slower than when defrosting is not required. Further still, during the defrosting mode, ambient conditions are the same as conditions where charge air cooler condensation is a large concern on boosted engines. When condensation accumulates in the intake system the potential for engine misfires and NVH issues increases.
The inventors herein have recognized that the heat generated at the HVAC system during a defrosting mode can be advantageously used during an engine cold-start to expedite warming of the charge air cooler and the engine. In one example, this may be achieved by a method for an engine comprising: responsive to a vehicle defrost condition, operating an air conditioner, and rejecting heat from a first cooling circuit to engine intake air, the first cooling circuit coupled to the air conditioner, a charge air cooler, and a radiator, the first cooling circuit not coupled to the engine. In this way, while the air conditioner is engaged to dehumidify the cabin during defrosting, the heat rejected by the air conditioner is advantageously used to expedite warming of the engine and the charge air cooler.
For example, an engine system may include a first cooling circuit coupled to an air conditioner (or HVAC system), a charge air cooler, a first coolant pump, and a radiator. The radiator may be coupled to the remaining components of the first cooling circuit via a thermostat valve such that when temperature of coolant flowing through the first cooling circuit is lower than a threshold, the thermostat valve remains closed and coolant flows through the circuit while bypassing the radiator. Then, when coolant temperature is above the threshold, the thermostat valve opens to allow coolant to flow through the radiator. As such, the first cooling circuit may constitute a low temperature loop. A second, different cooling circuit may include the engine and a fan, the second circuit constituting a high temperature loop. During vehicle defrosting conditions, the air conditioner (AC) may be operated to dehumidify the cabin air. Heat absorbed from the evaporator from the condensing cabin moisture during dehumidification is rejected to the water cooled AC condenser in the low temperature cooling circuit thereby warming the coolant. The first coolant pump may be operated to flow warmed coolant in the first cooling circuit through the AC (where heat is picked up) and then through a charge air cooler (CAC) while bypassing the radiator. By bypassing the low temperature radiator, no heat is lost to the atmosphere and the warm coolant is able to warm the CAC. The warm CAC in turn warms the aircharge flowing there-through. Once the coolant in the first cooling circuit is sufficiently hot (e.g., above a threshold), the thermostat valve may open and coolant may be pumped around the first cooling circuit through the radiator, allowing heat to be lost to the environment, and enabling temperature control of the first cooling circuit.
Expedited heating of the CAC provides multiple benefits. First, it expedites engine warm-up by heating the intake aircharge received in the engine, which in turn improves the efficiency of defrosting. Second, by increasing the temperature at the CAC, condensation issues at the CAC are reduced. In addition, low pressure EGR can be introduced earlier without condensation concerns. As such, once EGR is introduced, heat rejected by the EGR cooler into the second cooling circuit further expedites engine warm-up. In this way, defrost heat may be recovered and added to a CAC during cold ambient conditions to expedite warming of the CAC and engine. By operating the engine with warmer air, particulate matter (PM), CO and hydrocarbon (HC) emissions are reduced, and by extending the range of EGR operation, fuel economy benefits are also achieved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.